Prepregs are “pre-impregnated” composite fibers where a matrix material, such as an epoxy resin-containing material, is already present. The fibers often take the form of a weave and the matrix is used to bond them together and to other components during manufacture. The matrix is typically partially cured to allow easy handling; this is called B-Stage material and requires cold storage to prevent complete curing. Therefore, B-Stage prepregs are stored in cooled areas, as heat accelerates complete polymerization. Hence, an autoclave or oven is often required to complete the curing where manufacturing structures comprising prepreg layers or plies.
Prepregs allow for the impregnation of a fiber-containing material on a flat workable surface. Stacks of prepreg plies are then formed, with the stack then formed into a desired shape. Prepregs also allow one to impregnate a bulk amount of fiber and then store the prepreg in a cooled area for an extended period of time to cure later.
The use of conventional prepregs impacts the timing of manufacturing as the prepregs may begin to partially cure as they achieve room temperature, typically from a refrigerated state. In addition, the presence of the resin-containing material in the prepregs renders a surface tack to the prepregs that can present difficulties, for example, when prepregs are used in automated processes where residual resin over time can require significant down time for automated machine cleaning, etc. Further, when prepregs are laid up, or stacked into a configuration for part or component formation, the surface tack of the layers can present challenges to using prepregs in certain automated composite forming processes, and can lead to significant waste in terms of material, time and cost due to trimming that is required if, for example, misalignment of laminate layers (e.g. prepreg stacks) occurs in laminate composite part formation.